Implement run+? which would make increment within that sequence

[yarikoptic]

request by @dnkennedy

TODOs

• [ ] make sure does not break existing
• [ ] add tests for +? mode

[dnkennedy]

Is there something I should do regarding testing this?

[codecov[bot]]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.01% :warning:

Comparison is base (69c271e) 82.00% compared to head (e2223bb) 82.00%.

:exclamation: Current head e2223bb differs from pull request most recent head 38a80b5. Consider uploading reports for the commit 38a80b5 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #701 +/- ## ========================================== - Coverage 82.00% 82.00% -0.01% ========================================== Files 41 41 Lines 4130 4139 +9 ========================================== + Hits 3387 3394 +7 - Misses 743 745 +2 ``` | [Files Changed](https://app.codecov.io/gh/nipy/heudiconv/pull/701?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipy) | Coverage Δ | | |---|---|---| | [heudiconv/heuristics/reproin.py](https://app.codecov.io/gh/nipy/heudiconv/pull/701?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipy#diff-aGV1ZGljb252L2hldXJpc3RpY3MvcmVwcm9pbi5weQ==) | `84.68% <75.00%> (-0.20%)` | :arrow_down: |

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